Dental-investment compound.



JAMES JDAWKINS L. TENCH, 0F GAINESVILLE, FLORIDA.

DENTAL-INVESTMENT COMPOUND.

No Drawing.

To all whom it may concern:

Be it known that 1, JAMES D. L. TnNoH, a citizen of the United States, and a resident of Gainesville, in the county of Alachua and State of Florida, have invented a certain new and useful Improvement in Dental- Investmentv Compounds, of which the following is a specification.

My invention is an improvement in dental investment compounds, and has for its object to provide a compound of the character specified in the form of a dry impalpable powder, which may be made into a plastic condition by the addition of water, to provide an investment for surrounding a wax model, which is afterward burnt out by the use of heat, leaving a matrix for the metallic casting.

As is known, in preparing inlay fillings for teeth, a model in wax or the like is made of the cavity, and this model is inclosed in an investment compound. The model isthen melted or burnt away by heat, leaving a mold or form in which the gold or other metal may be cast. It will be obvious that any compound for this purpose should be of fine grain material to insure a smooth surface to the cast, but possessingsuflicient porosity to absorb the wax employed, and wherein there is no appreciable shrinkage under the 'high heat employed, nor surface cracks or checks, and which will be a good conductor of heat, so that the molten metal will not cool before it has run into and copied all the intricacies of the mold.

With this object in view I provide anompound which consists of a carborundum powder, about No. 3F in fineness, and one part of plaster of Paris, the two ingredients being thoroughly and uniformly mixed together in the form of a dry powder.

When it is desired to prepare the investment compound, the powder is mixed with water to the proper consistency for use. The com ound presents many advantages, among w ich may he named the uniformly fine and nearly impalpable form of powder so finely ground that it insures a smooth, nearly polished, surface to the cast. The compound, however, has sufiicient porosity, so that all the wax can be dissipated before the metal is cast, while at the same time there will be no appreciable shrinkage under Specification of Letters Patent.

Patented May 7, 191%.

Application filed August 10, 1916. Serial No. 114,243.

the high heat employed, nor will there be shrinkage, surface cracks, or checks. The compound is a good conductor of heat, so that the molten metal will not cool too quickly but will enter and fill all the intricacies of the mold.

The composition also provides an added edge strength to a tough body, so that it not only copies perfectly the fine feather margins represented in the Wax models, but is remarkably free from bumps and nodules which are so apparent in the ordinary compound, and Which are no small impediment, often causing much grinding in order to properly fit the cavity.

A most important feature of the compound is the element of time saved in making a cast. Usually from forty to sixty minutes are required in order to drive the moisture and the wax from the compound in the casting ring before the ring can be placed in the casting machine. With the present compound, however, the finished cast can be turned out in less than ten minutes. It is a fact that the Water in the compound may be driven out so rapidly by the applica tion of heat, that it boils at the top of the crucible or casting ring, yet the investment compound is not injured by the expanding gas since it may escape so rapidly.

It will be understood that the improved compound may be used with any type of casting machine. It is also suitable for use as an investment in all kinds of difficult soldering operations, such as backing up porcelain faced crowns and in making bridges. In use the compound is prepared by placing in the mixing bowl a tablespoonful of water; two moderately heaping teaspoonfuls of the compound are then added, and the compound is gently teased in the bowl until it is entirely and uniformly covered with water. Any excess water is poured ofi. The resultant mixture should have the consistency of new clabber.

I claim 1. A dental investment compound comprising carborundum powder and plaster of Paris in the ratio of two and one-half parts of the first to one part of the second, and thoroughly and intimately mixed in the form of a dry owder capable of becoming plastic on the a dition of water.

' 2. A dental investment compound composed Of a fine carborundum powder and posed of a fine carborundum powder and dry .plaster of Paris, intimately and uni- 10 dry plaster of Paris, intimately and uniformly mixed.

formly mixed, the carborundum being of 5 the fineness of N0. 3F, and being present DAWKINS TENCH' in the ratio of two and one-half parts to Witnesses: one of the plaster of Paris. GEO. P. MORRIS, I

3. A dental investment compound com- JOSEPH B. BROOKS. 

